Integrated circuit (IC) technologies are constantly being improved. Such improvements frequently involve scaling down device geometries to achieve lower fabrication cost, a higher device integration density, a higher speed, and better performance. Along with various advantages resulting from such a reducing geometry size, improvements are being made directly to IC devices, for example, an image sensor device.
Generally, an image sensor device includes an array (or grid) of pixels for detecting incident light and recording intensity (or brightness) of the incident light. Each pixel includes at least one photosensitive diode (hereinafter “photodiode”) configured to detect the incident light and convert the detected incident light into an electrical signal (e.g., a photocurrent/current signal), and a plurality of transistors (hereinafter “pixel transistors”) coupled to the photodiode that are collectively configured to process the electric signal(s) so as to record the intensity or brightness of the detected incident light.
To assess performance of the image sensor device, various characteristics of the image sensor device are generally considered, an important one of which is a quantum efficiency of the image sensor device. Such a quantum efficiency is typically determined by a “fill factor” of the image sensor device. The fill factor is calculated as a ratio of a chip area occupied by the photodiode(s) divided by a total chip area of the respective pixel. In conventional image sensor devices, however, at least one of the above-mentioned pixel transistors are planarly formed. That is, a respective gate feature of the at least one pixel transistor only laterally extends along a major surface of the pixel. When forming the gate feature in such a completely lateral fashion, the fill factor may be disadvantageously reduced since over a given chip area, a chip area available for disposing the photodiodes may be significantly reduced.
Thus, existing image sensor devices and methods to make the same are not entirely satisfactory.